docs: def helical_turbulent_fd_Mori_Nakayama(Re, Di, Dc):
      r'''Calculates Darcy friction factor for a fluid flowing inside a curved 
      pipe such as a helical coil under turbulent conditions, using the method of 
      Mori and Nakayama [1]_, also shown in [2]_ and [3]_.
          
      .. math::
          f_{curv} = 0.3\left(\frac{D_i}{D_c}\right)^{0.5}
          \left[Re\left(\frac{D_i}{D_c}\right)^2\right]^{-0.2}\left[1 
          + 0.112\left[Re\left(\frac{D_i}{D_c}\right)^2\right]^{-0.2}\right]
  
      Parameters
      ----------
      Re : float
          Reynolds number with `D=Di`, [-]
      Di : float
          Inner diameter of the coil, [m]
      Dc : float
          Diameter of the helix/coil measured from the center of the tube on one
          side to the center of the tube on the other side, [m]
  
      Returns
      -------
      fd : float
          Darcy friction factor for a curved pipe [-]
  
      Notes
      -----    
      Valid from the transition to turbulent flow up to 
      :math:`Re=6.5\times 10^{5}\sqrt{D_i/D_c}`. Does not use a straight pipe 
      correlation, and so will not converge on the
      straight pipe result at very low curvature.
  
      Examples
      --------
      >>> helical_turbulent_fd_Mori_Nakayama(1E4, 0.01, .2)
      0.037311802071379796
  
      References
      ----------
      .. [1] Mori, Yasuo, and Wataru Nakayama. "Study of Forced Convective Heat 
         Transfer in Curved Pipes (2nd Report, Turbulent Region)." International 
         Journal of Heat and Mass Transfer 10, no. 1 (January 1, 1967): 37-59.
         doi:10.1016/0017-9310(67)90182-2. 
      .. [2] El-Genk, Mohamed S., and Timothy M. Schriener. "A Review and 
         Correlations for Convection Heat Transfer and Pressure Losses in 
         Toroidal and Helically Coiled Tubes." Heat Transfer Engineering 0, no. 0
         (June 7, 2016): 1-28. doi:10.1080/01457632.2016.1194693.
      .. [3] Ali, Shaukat. "Pressure Drop Correlations for Flow through Regular
         Helical Coil Tubes." Fluid Dynamics Research 28, no. 4 (April 2001): 
         295-310. doi:10.1016/S0169-5983(00)00034-4.
      '''
      term = (Re*(Di/Dc)**2)**-0.2
      return 0.3*(Dc/Di)**-0.5*term*(1. + 0.112*term)